Optical scanning device

ABSTRACT

An optical scanning device directs a light beam emitted from a light source to a mirror of a mechanical deflector through a first optical system, deflects the light beam in a main scanning direction by causing the light beam to be reflected by a mirror surface of the mirror, the angle of the mirror surface changing due to rotation of the mirror, and directs the deflected light beam through a second optical system to a surface to be scanned moving in a sub-scanning direction, the light source, first optical system and mechanical deflector being contained in a housing. The mechanical deflector is held in the housing through a holding member, and, also, material of the housing is different in heat conductivity from the holding member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical scanning device loaded in an electrophotographic image forming apparatus or the like.

2. Description of the Related Art

An electrophotographic image forming apparatus such as a digital copier, a laser printer or the like has an optical scanning device which deflects a light beam from a laser light source in a main scanning direction through a deflector, and forms a beam spot on a surface of a photosensitive body (surface to be scanned) moving in a sub-scanning direction (perpendicular to the main scanning direction). Thus, the optical scanning device forms a latent image of an image to be output on the surface of the photosensitive body.

As the deflector of the optical scanning device, a mechanical deflector employing a polygon mirror, a galvano-mirror or the like is used in general.

FIG. 1 shows an example of configuration of an optical scanning device in the related art.

The optical scanning device 40 causes a light beam 42 emitted from a laser light source 41 to be incident on a polygon mirror 47 rotating at high speed through a first optical system 46 consisting of a coupling lens 43, a diaphragm 44 and a line-image forming optical system 45, and causes the light beam to be reflected by a mirror surface 47a of the polygon mirror 47, the angle of which surface changes with the rotation of the polygon mirror 47. Thereby, the light beam 42 is deflected in the main scanning direction, and, thus, performs scanning repeatedly.

The light beam 48 reflected by the polygon mirror 47 passes through a second optical system consisting of an fθ lens 49, a long-dimension lens 50 and a turning mirror 51, and is used to scan a surface 53 a (surface to be scanned) of a photosensitive body belt 53 moving in the sub-scanning direction.

At this time, the laser light source 41 is intensity-modulated according to an image to be output, and, thereby, an electrostatic latent image is formed on the surface 53 a of the photosensitive body belt 53 in a form of a dot pattern by the blinking light beam 48.

As mentioned above, a mechanical deflector employing a polygon mirror or a galvano-mirror is used as a deflector of an optical scanning device in general. Because each of the polygon mirror and galvano-mirror is driven by a motor, heat is generated by the motor when it is driving the mirror.

Recently, as an image output speed is increased, a driving speed of a deflector of an optical scanning device is increased. Thereby, a heat amount generated by the motor of the deflector increases. Accordingly, it becomes not possible to ignore influence thereof on other optical components (a light source, a coupling lens, a diaphragm, a line-image forming optical system, an fθ lens, a long-dimension lens, and so forth) contained in a housing of the optical scanning device together with the deflector.

Heat generated by the motor is transmitted to the respective optical components mainly through the housing. Thereby, the respective optical components are heated, and, thereby, problems may occur such as a shift of imaged position (focus shift), thickening of light beam, error of writing magnification, and so forth. As a result, image quality may be degraded.

Further, as a driving speed of a deflector is increased, a vibration generated thereby when the deflector is driven has come to be not able to be ignored. Accordingly, it has come to be not possible to use a plastic as a housing of an optical scanning device, and a metal has come to be employed therefor. Because metal has a heat conductivity larger than that of plastic, heat from a motor of a deflector comes to be more easily transmitted by the housing. As a result, other respective optical components come to be affected by the heat from the motor of the deflector more seriously. Accordingly, the above-mentioned problems occur more remarkably.

Further, recently, lenses and/or mirrors which are main components of optical systems of an optical scanning device come to be made by plastic, and are made to have spherical surfaces so that both high performance and low costs of the device come to be directed.

However, because plastic-made components are not superior in heat-resistant property in comparison to glass-made components, lenses and mirrors which are main components of optical systems are more seriously affected by heat from a motor.

Accordingly, the above-mentioned problems occur more remarkably.

In the related art, Japanese Laid-Open Patent Application No. 7-244249 discloses an idea for avoiding influence of heat from a deflector.

According to Japanese Laid-Open Patent Application No. 7-244249, a scanning lens is separated from other optical components (mainly a deflector) in a housing, and, thereby, shift of scanning position and change of diameter of light beam occurring due to shake of air surrounding the scanning lens are prevented. This technique is directed to eliminate influence of shake of air (air flow generated by the deflector) around the deflector due to rotation of a mirror of the deflector, basically.

However, according to this idea, although the deflector is separated from optical components such as the scanning lens, a turning mirror and so forth which direct light reflected by the deflector to a surface to be scanned, the deflector is not separated from other optical components such as a coupling lens, a diaphragm, a line-image forming optical system which direct a light beam to the deflector. Accordingly, those other optical components are affected by heat generated by the deflector.

As a result, in the housing, some optical components are affected by heat from the deflector, and the other optical components are not. Generally speaking, in order to prevent characteristics of respective optical components included in a optical system from shifting unevenly, design is made such that the entirety of the optical system is in a uniform temperature environment, and, when the temperature environment changes, the system can be corrected as a whole. Accordingly, when some optical components are in a different temperature environment, a design for correction with respect to environment change becomes difficult.

SUMMARY OF THE INVENTION

The present invention has been devised in consideration of the above-mentioned problems, and, an object of the present invention is to provide an opitcal scanning device using a mechanical deflector employing a polygon mirror or a galvano-mirror in which heat generated by the mechanical deflector is made to be not easily transmitted to other optical components contained in a housing together with the mechanical deflector, and, thereby, stable optical scanning without fluctuation due top temperature can be performed.

An optical scanning device according to the present invention directs a light beam emitted from a light source to a mirror of a mechanical deflector through a first optical system, deflects the light beam in a main scanning direction by causing the light beam to be reflected by a mirror surface of the mirror, the angle of the mirror surface changing due to rotation of the mirror, and directs the deflected light beam through a second optical system to a surface to be scanned moving in a sub-scanning direction, the light source, first optical system, mechanical deflector and second optical system being contained in a housing. The mechanical deflector is held in the housing through a holding member, and, also, material of the housing is different in heat conductivity from the holding member.

Thereby, it is hard for heat generated by the mechanical deflector to be transmitted to the housing. Accordingly, it is possible to prevent the other optical components contained in the housing together with the mechanical deflector from being heated, and to prevent the performance of the optical scanning device from being degraded due to temperature rise of those optical components.

It is preferable that heat conductivity of the housing is smaller than heat conductivity of the holding member holding the mechanical deflector which is a heat source.

Thereby, it is head for heat generated by the mechanical deflector to be transmitted to the housing. Accordingly, it is possible to more effectively prevent the other optical components contained in the housing together with the mechanical deflector from being heated, and to prevent the performance of the optical scanning device from being degraded due to temperature rise of those optical components.

An optical scanning device according to another aspect of the present invention directs a light beam emitted from a light source to a mirror of a mechanical deflector through a first optical system, deflects the light beam in a main scanning direction by causing the light beam to be reflected by a mirror surface of the mirror, the angle of the mirror surface changing due to rotation of the mirror, and directs the deflected light beam through a second optical system to a surface to be scanned moving in a sub-scanning direction, the light source, first optical system, mechanical deflector and second optical system being contained in a housing. The mechanical deflector is directly mounted to the housing, and, also, material of the housing has heat conductivity smaller than that of a part of the mechanical deflector in contact with the housing.

Thereby, it is hard for heat generated by the mechanical deflector to be transmitted to the housing. Accordingly, it is possible to prevent the other optical components contained in the housing together with the mechanical deflector from being heated, and to prevent the performance of the optical scanning device from being degraded due to temperature rise of those optical components.

It is preferable that the mechanical deflector is covered by a cover having an optical window, and, thereby, an air flow occurring due to rotation of the mirror is kept within the cover.

Thereby, it is possible to prevent temperature rise of the other optical components due to convection of heated air, and, thereby, to prevent the performance of the optical scanning device from being degraded. Further, because an air flow occurring due to rotation of the mirror is prevented from reaching the other optical components, shift of scanning position, change of diameter of light beam and so forth occurring due to shake of air in the proximity of those optical components can be prevented.

It is preferable that a cooling part forcibly cooling the mechanical deflector is provided.

Thereby, it is possible to prevent the housing and air in the housing from being heated by heat from the mechanical deflector, and to prevent temperature rise of the other optical components.

Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a configuration of an optical scanning device in the related art;

FIG. 2A shows a plan view of an optical scanning device in each of first and second embodiments of the present invention;

FIG. 2B shows a side elevational sectional view of the optical scanning device shown in FIG. 2A;

FIG. 3 shows a graph of relationship between a motor speed of a polygon scanner and a temperature of motor case thereof;

FIG. 4 illustrates a variant embodiment of the first embodiment shown in FIGS. 2A and 2B in which a heat insulating member is inserted between a holding member holding the polygon scanner and a housing bottom plate;

FIG. 5A shows a plan view of an optical scanning device in a third embodiment of the present invention;

FIG. 5B shows a side elevational sectional view of the optical scanning device shown in FIG. 5A;

FIG. 6 illustrates a fourth embodiment of the present invention in which a polygon mirror of the polygon scanner is covered by a cover having an optical window; and

FIG. 7 illustrates a fifth embodiment of the present invention in which a cooling part forcibly cooling the polygon scanner is provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the accompanying figures, the same reference numerals are given to the same parts/components, and duplicated description of which is omitted.

FIG. 2A shows a plan view (a state in which a cover 20B is removed from a housing body 20A) of a first embodiment of an optical scanning device according to the present invention, and FIG. 2B shows a side elevational sectional view of the optical scanning device shown in FIG. 2A.

The optical scanning device 1 directs a light beam (light flux) 3 a emitted from a laser light source 2 through a first optical system 7 to a polygon mirror 9 of a polygon scanner 8 which is a mechanical deflector, and causes the light beam to be reflected by a mirror surface 9 a, the angle of which changes with rotation of the polygon mirror 9. Thereby, the light beam is deflected in a main scanning direction (the direction of the arrow A shown in FIG. 2A). At the same time, the deflected light 3 b is directed through a second optical system 13 to a surface 14 a (surface to be scanned) of a photosensitive body drum 14 which rotates in a sub-scanning direction (the direction of the arrow B shown in FIG. 2B). Thereby, optical scanning of the surface 14 a is performed.

It is noted that, as an image output speed is increased recently, a combination of a plurality of light sources, a semiconductor laser array or the like comes to be used as the light source device of such an optical scanning device.

The laser light source 2, first optical system 7, polygon scanner 8 and second optical system 13 are contained in a single housing 20.

The first optical system 7 includes a coupling lens 4, a diaphragm 5 and a line-image forming optical system 6.

The second optical system 13 includes an fθ lens 10, a long-dimension lens 11 and a turning mirror 12.

The housing 20 consists of the housing body 20A in which the laser light source 2, first optical system 7, polygon scanner 8 and second optical system 13 are set and the cover 20B which covers a top opening of the housing body 20A.

A light beam exit window 21 is formed in a bottom of the housing body 20A. The light beam exit window 21 is closed by a transparent glass plate 22 for preventing dust, toner and so forth from entering the housing 20 therethrough.

The laser light source 2 emits the divergent light beam 3 a. The light beam 3 a from the laser light source 2 passes through the coupling lens 4 so as to be transformed into an approximately parallel light flux, and, is reduced in diameter to a predetermined light flux diameter by the diaphragm 5. Then, from the thus-obtained light flux, a line-like image extending in the main scanning direction is formed on the mirror surface 9 a of the polygon scanner 8 by the line-image forming optical system 6 having refracting power in the sub-scanning direction.

It is also possible that the light beam 3a from the laser light source 2 is transformed into a divergent light flux or a convergent light flux by passing through the coupling lens 4.

The polygon scanner 8 includes the polygon mirror 9 and a motor 16 which rotates at high speed the polygon mirror 9 at a uniform velocity, and deflects an incident light flux at a uniform angular velocity.

The light beam (deflected light) 3 b reflected by the polygon mirror 9 is incident on the turning mirror 12 after passing through the fθ lens 10 and long-dimension lens 11. Then, the incident light beam is reflected downward by the turning mirror 12, then, exits from the housing 20 through the light beam exit window 21, and, then, is incident on the surface 14 a of the photosensitive body drum 14.

At this time, the laser light source 2 is intensity-modulated according to an image to be output, and, thereby, an electrostatic latent image of the output image is written to the surface 14 a of the photosensitive body drum 14 in a form of a dot pattern by the blinking light beam 3 b.

As the fθ lens 10 and long-dimension lens 11, optical components molded of plastic material are used.

Further, a synchronization detecting system 30 is provided. The synchronization detecting system 30 includes a synchronization sensor 31, and an imaging component 32 and a mirror 33 which direct the reflected light flux from the polygon scanner 8 to the synchronization sensor 31.

As described above, in the polygon scanner 8, the motor 16 rotates the polygon mirror 9 at high speed. Accordingly, the motor 16 generates heat when driving the polygon mirror 9.

FIG. 3 shows a graph of a temperature rise amount (a rise amount from the temperature at the start of measurement) of a motor case 16a with respect to a motor speed in a case where the polygon scanner 8 is measured solely.

From the graph, it can be seen that the temperature rises as the motor speed increases. Further, the rise rate is not linear, but the rise rate increases as the motor speed increases. In this experiment, the motor case 16 a is made of aluminum alloy.

The polygon scanner 8 is contained in the housing 20 in a condition in which it is disposed on the bottom plate 20Aa of the housing body 20A together with the other optical components such as the laser light source 2, coupling lens 4, diaphragm 5, line-image forming optical system 6, fθ lens 10, long-dimension lens 11, turning mirror 12 and so forth.

Accordingly, when heat generated by the motor 16 of the polygon scanner 8 was transmitted by the housing 20 to the other respective optical components, and, thereby, those optical components were heated, degradation (shift of imaging position, thickening of light beam, enlargement of magnification error and so forth) of performance of the optical scanning device 1 might occur, and image quality might be degraded.

According to the first embodiment of the present invention, the housing body 20A and a holding member 23 which holds the polygon scanner 8 are made to be separate parts, and the polygon scanner 8 is held in the housing 20 through the holding member 23. The material of the housing 20 is made to be different in heat conductivity from the material of the holding member 23. Thereby, the bottom plate 20Aa of the housing body 20A is separated from the polygon scanner 8, and, as a result, heat generated by the polygon scanner 8 is not easily transmitted to the housing body 20A.

In order that heat generated by the polygon scanner 8 is not easily transmitted to the housing body 20A further positively, it is preferable to prevent the bottom plate 20Aa of the housing body 20A from coming into contact with the holding member 23 by a space provided therebetween. In this case, in order to prevent fine particles such as dusts or toner from entering the housing 20 through the space between the holding member 23 and bottom plate 20Aa, a heat insulating material 24 or the like may be inserted between the holding member 23 and bottom plate 20Aa, as shown in FIG. 4. Thereby, it is possible to obtain both dust proof function and heat insulating function.

According to a second embodiment of the present invention, the material of the housing 20 has the heat conductivity smaller than that of the material of the holding member 23. When the heat conductivity of the housing 20 is smaller than the heat conductivity of the holding member 23 holding the polygon scanner 8 which is a heat source, heat from the polygon scanner 20 is not easily transmitted to the housing 20. Accordingly, it is possible to effectively prevent the other respective optical components from being heated. As a result, it is possible to prevent performance of the optical scanning device 1 from being degraded.

For example, in a case where aluminum is used as the material of the holding member 23 holding the polygon scanner 8, it is possible that heat generated by the polygon scanner 8 is not easily transmitted to the housing 20 as a result of using iron or steel having the heat conductivity smaller than that of aluminum as the material of the housing 20. The following table shows typical materials and heat conductivity of each thereof:

Heat Conductivity Material (W/m · k) Aluminum 238 Brass 117 Steel (Cu) 49.3 Steel (Ni—Cr) 34.5 Steel (Stainless) 15.7 Iron 89.5 Copper 399

According to a third embodiment of the present invention, as shown in FIGS. 5A and 5B, the polygon scanner 8 is directly mounted to the housing body 20A, and, also, the material of the housing 20 is made to be one having the heat conductivity smaller than those of the materials of contacting parts, that is, the motor case 16 a and a mounting plate 8 a.

Accordingly, in a case where the polygon scanner 8 is directly mounted to the housing body 20A, heat from the polygon scanner 8 is not easily transmitted to the housing 20 when the heat conductivity of the housing body 20A is smaller than the heat conductivities of the motor case 16 a and mounting plate 8 a. As a result, it is possible to effectively prevent temperature rise of the other respective optical components, and to prevent the performance of the optical scanning device 1 from being degraded.

Thus, by causing heat generated by the polygon scanner 8 to be not easily transmitted to the housing body 20A, it is possible to prevent the other optical components in the housing 20 from being heated due to heat conduction through the housing body 20A.

However, when the polygon mirror 9 rotates at high speed, surrounding air is stirred, and, thereby, convection of air occurs. As a result, heated air surrounding the motor 16 reaches the proximity of the other optical components through the air convection, and, the other optical components are heated thereby.

In order to prevent air convection due to rotation of the polygon mirror 9 from occurring, it is preferable to cover the polygon mirror 9 of the polygon scanner 8 by a cover 26 having an optical window 25, as shown in FIG. 6, as in a fourth embodiment of the present invention. Thereby, it is possible to keep an air flow occurring due to rotation of the polygon mirror 9 within the cover 26.

As a result of the cover 26 spatially separating the polygon mirror 9 from the other optical components, when air surrounding the polygon mirror 9 is stirred, influence thereof is prevented from extending to the outside of the cover 26. Accordingly, temperature rise of the other optical components by heated air is prevented. Further, because an air flow occurring due to rotation of the polygon mirror 9 does not reach the proximity of the fθ lens 10, long-dimension lens 11, turning mirror 12 and so forth, shift of scanning position, change of diameter of light beam and so forth occurring due to shake of air in the proximity of those optical components can be prevented.

According to a fifth embodiment of the present invention, by positively cooling the motor case 16 a or the holding member 23 of the polygon scanner 8 by a cooling part 27 as shown in FIG. 7, it is possible to lower the temperature of the polygon scanner 8 itself which is a heat source, or the holding member 23. Thereby, it is possible to prevent the housing 20 and air in the housing 20 from being heated by heat from the polygon scanner 8, and to prevent temperature rise of the other optical components.

As the cooling part 27, a cooling fan, a Peltier device or the like can be employed.

However, when the cooling fan is used as the cooling part 27, it is preferable that the outer surface of the motor case 16 a which is a heat source, or the like is forcibly cooled from the outside of the housing 20 in order to prevent air convection from occurring inside of the housing 20.

Although the optical scanning devices employing the polygon scanners have been described, the present invention can also be applied to optical scanning devices including mechanical deflectors employing galvano-mirrors.

The present invention is not limited to the above-described embodiments, and variations and modifications may be made without departing from the scope of the present invention.

The present application is based on Japanese priority application No. 11-338811, filed on Nov. 29, 1999, the entire contents of which are hereby incorporated by reference. 

What is claimed is:
 1. An optical scanning device directing a light beam emitted from a light source to a mirror of a mechanical deflector through a first optical system, deflecting the light beam in a main scanning direction by causing the light beam to be reflected by a mirror surface of said mirror, the angle of said mirror surface changing due to rotation of said mirror, and directing the deflected light beam through a second optical system to a surface to be scanned moving in a sub-scanning direction, said light source, first optical system, mechanical deflector and second optical system being contained in a housing, wherein said mechanical deflector is held in said housing through a holding member, a material of said housing is different in heat conductivity from said holding member, and a part of said holding member is exposed to an outside of said housing.
 2. The optical scanning device as claimed in claim 1, wherein heat conductivity of said housing is smaller than heat conductivity of said holding member.
 3. The optical scanning device as claimed in claim 1, wherein said mechanical deflector is covered by a cover having an optical window, and, thereby, an air flow occurring due to rotation of said mirror is kept within said cover.
 4. The optical scanning device as claimed in claim 1, wherein a cooling part forcibly cooling said mechanical deflector is provided. 